Compaction of Lunar‐Type Soil

Soil plays an important role in the construction of foundations of roads and buildings. The utilization of soil traditionally involves the compaction of the in‐situ or previously loosened material to achieve a desired strength. The paper reports an initial investigation on the effect of the percentage of fines on the densification and strength of lunar‐soil simulant. The results of vibratory and static compaction tests in the laboratory suggest that the amount of fines should be reduced from the existing 50% that is typical for lunar regolith. The measurement of density and cone resistance of soil mix with only 10% showed large differences when compared to soils with 30% or 50% fines. No attempt has been made to find optimal soil mixes for compaction.     

BCD: A Soil Modulus Device for Compaction Control

There is a trend toward using the modulus as an alternative to dry density in compaction control because of the undesirable nuclear source in the current field density gage and because a modulus is often used in the design of roadway bases and compacted fills. The Briaud compaction device (BCD) is a new instrument used to obtain a soil modulus in only a few seconds; it consists of leaning on a rod equipped with a thin circular metal plate at the bottom end and recording the bending of that plate under a standard load. This article describes the theory and the experiments that have been performed to validate the new instrument. This validation is based on a comparison to a simple plate test and on a numerical simulation of the BCD test. A recommended procedure is outlined in the conclusions. The BCD is used in the lab on top of the soil in the Proctor mold to obtain the lab modulus versus water content curve and select a target value. Then the BCD is used in the field to verify that the target modulus has been achieved.     

Canal Seepage Reduction by Soil Compaction

Simple in situ vibratory soil compaction of earth lined canals was tested to determine the impact on seepage losses. Commercial equipment was used for vibratory compaction of long sections of five irrigation district earthen canals. Ponding tests were conducted before and after compaction. When the sides and bottoms of the canals were compacted, seepage reductions of about 90% were obtained; reductions of 16–31% were obtained when only sides were compacted.     

Influence of Clod-Size and Structure on Wetting-Induced Volume Change of Compacted Soil

Volume changes due to wetting may occur in naturally deposited soils as well as earthen construction (e.g., compacted fills or embankments). Depending on the stress level, some soils exhibit increase in volume upon wetting (swell) while others may exhibit decrease in volume upon wetting (collapse). The work described in this paper focused on wetting-induced volume changes in compacted soils. Motivation for this work stemmed from observations of earthen structures that exhibit problematic behavior under wetting conditions, even though soils were compacted to engineering specifications (i.e., at or above minimum density and within moisture content ranges). Not only is this problematic behavior a concern but also the laboratory tests used to predict settlement of constructed facilities may not properly model the actual behavior of soil compacted under field conditions. For example, settlements experienced by compacted fills may be different from settlement predictions based on one-dimensional oedometer tests. These differences are partly related to the variations in the soil structure in tested specimens that arise because soil clods compacted in the laboratory are smaller than soil clods compacted in the field. The term “soil structure” includes the combined effects of soil fabric and interparticle forces. “Fabric” generally refers to the geometric arrangement of particles, whereas interparticle forces include physical and physicochemical interactions between particles. The soil structure in this case is associated with specimen preparation methods and is influenced by several factors including soil composition (including pore water chemistry), compaction method, clod sizes, initial moisture condition of clods, dry density or void ratio, and compaction moisture content. A laboratory research study was conducted to investigate the influence of variations in clod-size and structure on one-dimensional volume change, with emphasis on wetting-induced volume change, for nine different fine-grained soils. The results of the study suggest that the influence of structure in one-dimensional oedometer tests depends on soil type and nature of the clods in the compacted soil. Clayey soils appear to be influenced more by differences in structure, whereas silts or clayey sands of low plasticity (PI<10) do not appear to suffer as much from structure effects in one-dimensional oedometer tests. This is attributed to more extensive clod development in clayey soils. Furthermore, the moisture condition of clods appears to have an important influence on volume change behavior.     

Field Monitoring of Roller Vibration during Compaction of Subgrade Soil

A field investigation was carried out with an instrumented vibratory roller compactor to explore the relationship between vibration characteristics and underlying soil properties, namely soil stiffness. The roller was outfitted with instrumentation to monitor drum and frame acceleration, as well as eccentric excitation force. Multiple consecutive passes were performed over six test beds on an active earthwork construction site to capture changes in roller vibration during compaction. Using lumped parameter vibration theory, soil stiffness was extracted from the roller data (drum and frame acceleration and drum phase lag). Both drum acceleration and drum phase lag were found to be very sensitive to changes in underlying soil stiffness. The drum–soil natural frequency of the coupled roller–soil system varied considerably and increased with compaction-induced soil stiffening. Phase lag always decreased with increasing soil stiffness, whereas drum acceleration trends depended on whether the excitation frequency was less than or greater than resonance. Roller-determined soil stiffness was found to be a function of the eccentric force, and heterogeneity in moisture, lift thickness, and underlying stiffness has a considerable affect on roller vibration behavior. When used as a proof roller, the instrumented roller identified soft areas in the embankment that were not identified by a static proof roll test.     

Soil Water Content and Dry Density by Time Domain Reflectometry

Soil water content and dry density are two important properties for compaction quality control. This paper presents a new method for determining soil water content and dry density using a single time domain reflectometry test, which is an improvement over that designated by ASTM D6780. This new method is based on simultaneous measurement of apparent dielectric constant and bulk electrical conductivity on the same soil sample. Calibration equations correlate these two parameters with soil gravimetric water content and dry density, which are simultaneously solved after adjusting field-measured conductivity to a standard conductivity. The method compensates for temperature effects. The test process takes about 3 min and all calculations are automated. Testing may be done in situ using a special probe that provides sufficient sampling volume or in a compaction mold adapted to form a probe. Laboratory and field tests results show this one-step method is a fast, accurate, and safe method for construction quality control.     

Soil Moisture Flow Modeling with Water Uptake by Plants (Wheat) under Varying Soil and Moisture Conditions

A variably saturated soil moisture flow model is developed for planted soils with depth varying properties by incorporating a nonuniform macroscopic root water uptake function. The model includes spatial and temporal variation of the root density with dynamic root growth for simulating water uptake by plants along with the impact of soil moisture availability. The governing partial differential moisture flow equation integrated over the depth with a plant water uptake term is solved numerically by the implicit finite difference method using an iterative scheme. The model is first tested for barren soils for two profiles considering constant and depth varying soil characteristics under constant inflow condition. The results obtained are later tested with experimental data available in the literature. A nonuniform plant water uptake term is subsequently incorporated in the model and water uptake by wheat plants under different soil moisture availability conditions is studied. Finally, the moisture flow model is validated with field data of rain fed wheat (Triticum aestivum) using a dynamic root growth model for a layered root zone soil profile. The simulated soil moisture regime of the layered root zone shows a reasonably good agreement with the observed data.     

Effects of Magnetized Water and Irrigation Water Salinity on Soil Moisture Distribution in Trickle Irrigation

Magnetized water is obtained by passing water through a strong permanent magnet installed in or on a feed pipeline. This study was performed at Gorgan Agricultural and Natural Resources Research Center, Gorgan province, Iran, to investigate soil moisture distribution under trickle irrigation. Two main treatments of magnetic and nonmagnetic water and three subtreatments of irrigation water salts, including well water as a control, 200-ppm calcium carbonate, and 400-ppm calcium carbonate were used. The experiment was laid out with a complete randomized block design with three replications. Soil moisture distribution around the emitters were measured 24?h after irrigation during the 3-month irrigation period. The results showed that the mean soil moisture contents at depths of 0–20, 20–40, and 40–60?cm below the emitter for the magnetized irrigation water treatment were more than the nonmagnetized irrigation water treatment, and the differences were significant at the 5% level. The irrigation with magnetic water as compared with the nonmagnetic water increased soil moisture up to 7.5%, and this increase was significant at the 1% level. The effect of irrigation water salinity on soil moisture was significant. The highest soil moisture content was from the 400-ppm calcium carbonate subtreatment. The use of magnetized water for irrigation is recommended to save irrigation water.     

Establishing Soil-Water Characteristic Curve of a Fine-Grained Soil from Electrical Measurements

Application of a pressure membrane extractor (PME) to establish soil-water characteristic curve (SWCC) of fine-grained soils, in 0–1,500 kPa range, is well established. However, this technique requires testing of several identical specimens, corresponding to same or different pressure(s), and their subsequent removal from the PME chamber for moisture content determination. This turns out to be a cumbersome process and even the results are considered less accurate, by the research fraternity. This is mainly due to the fact that removal of the specimen before equilibration time may not incorporate the influence of the applied pressure, precisely. This calls for the development of an alternate technique that can be employed for measuring the instantaneous moisture content of the specimen when it is pressurized, sequentially, without removing it from the PME chamber. In this context, the utility of electrical measurements (i.e., the voltage) across two points in the specimen for determining moisture content was investigated and its details are presented in this paper. This technique has been found to be quite promising and hence can be employed for acquisition of the data which would yield the moisture content of the specimen, without removing it from the PME chamber, easily and quickly. Validity of the methodology has been demonstrated by comparing the obtained SWCC vis-à-vis those obtained by conducting studies using a dewpoint potentiameter, WP4, and by employing the fitting function and a pedo-transfer function available in the SoilVision database.     

Estimation of Soil–Water Characteristic Curve of Clayey Till Using Measured Pore-Size Distributions

The soil–water characteristic curve (SWCC) of fine-grained soils is usually determined experimentally. In the design of mine waste covers and landfill liners, the unsaturated hydraulic conductivity function, k(h), is often derived theoretically from the measured SWCC. Implicit in these derivations is the transformation of the SWCC to a pore-size distribution (PSD), typically assumed to be constant and monomodal. However, PSD measurements of a clayey till compacted at various water contents after compaction, after flexible-wall permeability testing and before and after SWCC tests show that the PSD of the same material varies significantly under the stated physical conditions. Predictions of the SWCCs using PSDs measured both before and after the SWCC tests significantly underpredicted the values measured. By applying a simple transformation to the PSD to account for the scaling effect from the porosimetry samples (approximately 1 g dry weight) to the SWCC test samples (approximately 200 g dry weight), the predicted SWCCs were found to envelop the measured values. A simple model that simulates the change in PSD during the SWCC test predicted water contents close (1% root mean square error) to the measured SWCCs.     

Effects of Soil Water Salinity on Field Soil Hydraulic Functions

Unsaturated soil hydraulic parameters and functions used in numerical models to simulate water flow and solute transport in the unsaturated zone are generally considered invariant of soil water salinity levels. This study uses 5 years of field soil water salinity levels at three observation sites from the Land Retirement Demonstration Project (LRDP) (20069) located in western Fresno County, California, to test the hypothesis that field unsaturated soil hydraulic properties are also a function of soil water salinity level. The HYDRUS-1D software package for simulating one-dimensional (1D) movement of water, heat, and multiple solutes in variably saturated media, and Parameter Estimation (PEST), a model-independent parameter optimizer, is used to optimize the soil hydraulic parameters and downward bottom flux corresponding to three different average soil salinity levels at each site. The results show that at the same pressure head, soil water content is less with higher soil water salinity as compared with lower soil water salinity. It is thus concluded that the use of soil water salinity invariant soil water hydraulic parameters in numerical modeling can seriously compromise predictions, especially for a variable soil water salinity environment.     

Dynamic Compaction of Collapsible Soils Based on U.S. Case Histories

Dynamic compaction (DC) is an economical approach for mitigating the hazard posed by collapsible soils particularly when they are deeper than 3–4 m. In this paper, case histories are provided for 15 projects at 10 locations in the United States where collapsible soils were treated with DC. For each site the soil properties, compaction procedures, and subsequent improvement are summarized. Although cohesionless and low-plasticity collapsible soils were successfully compacted, clay layers in the profile appeared to absorb energy and severely reduced compaction effectiveness. Correlations are presented for estimating the maximum depth of improvement, the degree of improvement versus depth, the depth of craters, and the level of vibration based on measurements made at the various sites. The compactive energy per volume was typically higher than for noncollapsible soils because collapsible soils are usually loose but relatively stiff. The maximum depth of improvement was similar to that for noncollapsible soils; however, significant scatter was observed about the best-fit line. Improvement was nonuniform with nearly 80% of the total improvement occurring within the top 60% of the improvement zone. The crater depth was related to a number of factors besides the drop energy including the number of drops, drop spacing, and contact pressure. The peak particle velocities were typically lower than those for noncollapsible soils at shorter distances, but the vibrations attenuated more slowly with distance.     

Seismic Performance of a River Dike Improved by Sand Compaction Piles

Sand compaction piling is one of the commonly used countermeasures for earthquake liquefaction hazard of river dikes. This paper presents a case study of the performance of an instrumented dike in northeast Japan that was improved by sand compaction piles and subjected to the 2003 Northern Miyagi Earthquake, with the aim to better understand the effectiveness of this ground improvement method. Simulation has been carried out by means of a fully coupled numerical procedure which employs a sophisticated cyclic elastoplastic constitutive model and the updated Lagrangian algorithm. Comparisons between the field measurements and the computed responses, including the time histories of accelerations and pore-water pressures at different locations, show reasonably good agreement. Numerical simulation has also been made of the same dike but without ground improvement to identify the effects of sand compaction piles in altering the performance of the dike. The study demonstrates that the comprehensive numerical procedure is a promising tool for development of seismic performance-based design of earth structures.     

Geostatistical Analysis for Spatially Referenced Roller-Integrated Compaction Measurements

An approach to quantify nonuniformity of compacted earth materials using spatially referenced roller-integrated compaction measurements and geostatistical analysis is discussed. Measurements from two detailed case studies are presented in which univariate statistical parameters are discussed and compared to geostatistical semivariogram modeling parameters and analysis. The univariate and geostatistical parameter values calculated from the roller-integrated measurements are also compared to traditional spot test acceptance criteria. Univariate statistical parameter values based on roller-integrated measurement values provide significantly more information than traditional point measurements, while geostatistics can be used to identify regions of noncompliance and prioritize areas for rework.     

Earth Pressure due to Vibratory Compaction

This paper presents experimental data on the variation of lateral earth pressure against a nonyielding retaining wall due to soil filling and vibratory compaction. Air-dry Ottawa sand was placed in five lifts and each lift was compacted to achieve a relative density of 75%. Each compacted lift was 0.3?m thick. The instrumented nonyielding wall facility at National Chiao Tung University in Taiwan was used to investigate the effects of vibratory compaction on the change of stresses at the soil-wall interface. Based on the experimental data it has been found that, for a compacted backfill, the vertical overburden pressure can also be properly estimated with the traditional equation σv = γz. The effects of vibratory compaction on the vertical pressure in the backfill were insignificant. On the vertical nonyielding wall, extra horizontal earth pressure was induced by vibratory compaction. After compaction, the lateral earth pressure measured near the top of the wall was almost identical to the passive Rankine pressure. It is concluded that as the cyclic compacting stress applied on the surface of the backfill exceeded the ultimate bearing capacity of the foundation soil, a shear failure zone would develop in the uppermost layer of the backfill. For a soil element under lateral compression, the vertical overburden pressure remained unchanged, and the horizontal stress increased to the Rankine passive pressure. It was also found that the compaction-influenced zone rose with the rising compaction surface. The horizontal earth pressure measured below the compaction-influenced zone converged to the Jaky state of stress.     

Soil Water Content Monitoring Using Electromagnetic Induction

The use of electromagnetic (EM) induction measurements was evaluated to predict water content in the upper 1.50 m of a prototype engineered barrier soil profile designed for waste containment. Water content was monitored with a neutron probe, and bulk soil electrical conductivity was monitored with a Geonics EM38 ground conductivity meter at ten locations at approximately monthly intervals over a three-year period. A simple linear regression model accurately predicted average volumetric water content of the profile at any location at any time (R2 = 0.80,σ = 0.009) and spatially averaged volumetric water content over the entire area at any time (R2 = 0.99,σ = 0.003). Although some temporal drift was present in the model residual values, the impact on predicted water content was negligible. Therefore, once the model is calibrated with the neutron probe over a sufficient range of water contents, further neutron probe measurements may not be necessary. EM induction has several advantages over traditional water content monitoring techniques, including nonradioactivity, speed and ease of use over larger areas, and noninvasive character.     

Experimental Study on the Performance of Approach Slabs under Deteriorating Soil Washout Conditions

In the U.S. bridge design practice, an approach slab is commonly provided to facilitate a smooth transition from the highway pavement to the bridge deck. Maintenance of bridge approaches often necessitates the repair or replacement of approach slabs owing to damage from heavy traffic loads, washout of fill materials, and settlement of the approach embankment. Approach slab damage because of embankment settlement is considered a more common problem and has been extensively investigated in the literature. In this paper, performance of the approach slab degraded by void formation underneath the slab is examined by load testing. Full-size approach-slab specimens were tested under increasing magnitude up to four times AASHTO HS20-44 design truck loads. The test matrix included four slab specimens with the following details: (1)?conventional steel reinforcement representative of current California design; (2)?steel reinforcement replaced by a double-layer pultruded fiber-reinforced polymer grating; (3)?steel reinforcement replaced by glass fiber-reinforced polymer rebars; and (4)?incorporation of steel and polyvinyl alcohol fibers in the concrete mix and removal of top longitudinal and transverse steel. Results indicated that the slabs show satisfactory performance under standard HS20-44 design truck load. Tests also revealed that these slabs exhibited similar performance in terms of stiffness, deformation, and crack pattern when fully supported, but registered noticeable difference in performance under deteriorating soil washout conditions. The fiber-reinforced concrete slab in general showed the best crack control and the smallest deflection and end rotation among the four slabs.     

Estimating Compaction of Cohesive Soils from Machine Drive Power

To evaluate roller-integrated machine drive power (MDP) technology for predicting the compaction parameters of cohesive soils considering the influences of soil type, moisture content, and lift thickness on machine power response, a field study was conducted with 15-m test strips using three cohesive soils and several nominal moisture contents. Test strips were compacted using a prototype CP-533 static padfoot roller with integrated MDP technology and tested using various in situ compaction measurement devices. To characterize the roller machine-soil interaction, soil testing focused on measuring compaction parameters for the compaction layer. Variation in both MDP and in situ measurements was observed and attributed to inherent variability of the compaction layer and measurement errors. Considering the controlled operations to create relatively uniform conditions of the test strips, measurement variability observed in this study establishes a baseline for acceptable variation in production operations using MDP technology in cohesive soils. Predictions of in situ compaction measurements from MDP were found to be highly correlated when moisture content and MDP-moisture interaction terms were incorporated into regression models.